In recent years, various types of display apparatuses have been developed to display two-dimensional information such as a digitized image. In an often used method, using a form of the display wherein a great number of display elements are arranged in a two-dimensional array, a display element is made to correspond to each of the pixels constituting the two-dimensional information to be displayed. In response to each pixel value, an electric signal is sent for drive and display.
Thus, each display element is required to provide a quick response necessary for display based on an adequate drive signal, and to be capable of being produced in a downsized configuration to maintain the overall quality (including resolution). It is also required to provide high density arrangement and a large screen display without involving manufacturing difficulties or high costs.
In the meantime, the conventional color display element has required to three sub-pixels corresponding to R, G and B for color display using the primary colors of R, G and B (red-green-blue). To be more specific, it has been required that three display elements are arranged side by side in order to represent one original pixel. This involved a problem of a low aperture ratio, namely, a smaller display area rate per area occupied by a pixel, and poorer display efficiency of each of the R, G and B.
Thus, what was desired was the capability of displaying any one of the R, G and B colors, not the capability of displaying an independent display element in one color. To meet this requirement, a technique as disclosed in for example the following documents was developed to ensure that the colors that could be displayed by the independent display element is variable, without deteriorating the aforementioned required performances:
Unexamined Japanese Patent Application Publication (JP-A) No. H5-134266; and
Oguchi and Hatsuzawa “A Study of Electrostatically driven display device” (online), Apr. 1, 2006, Precision Engineering Laboratory, Tokyo Institute of Technologies, (Searched on Apr. 28, 2006), Internet <URL: http://www.pme.pi.titech.ac.jp/research/old/display/display.htm>.
In one of the methods for displaying a desired color of the R, G and B by one pixel, viz., by an independent display element, a chiral nematic liquid crystal is layered in three layers. To be more specific, without using the side-by-side arrangement, the RGB colors are displayed using stacked three layers, whereby a desired color of the R, G and B is displayed by one pixel.
However, since a plurality of substrates are to be utilized, this method involves a problem of the manufacturing process becoming complicated. Further, to display a high definition image, a film substrate or thin glass plate must be utilized from the viewpoint of parallax. These difficulties have not been overcome.
A solution to this problem is the technique of display element proposed in the first document (JP-A H5-134266), whereby a plurality of thin films having different refractive indexes are sandwiched by a pair of electrodes, and voltage is applied, so that the refractive index of the liquid crystal layer is changed and a desired color of R, G and B is displayed by one pixel. In this technique, a plurality of thin films having different refractive indexes are used as an optical interference filter. The refractive index is changed by an electric field, whereby the reflection wavelength or transmission wavelength by an interference filter is changed, and the displayed color is changed.
However, in this method, a high-fluidity liquid crystal film must be formed to a thickness of about 100 nm in order to perform the function of an interference filter. This involves difficulties in the manufacturing process and is not suited for formation of a large-area display element in particular.
According to the technique proposed in the second document, there is provided the display element formed by layering a micromachined half mirror and fixed mirror (silicon substrates) through gaps. In the display element, a half mirror support section is driven by an actuator whereby the distance between the half mirror and fixed mirror is changed, and a desired color of the R, G and B is displayed by one pixel. This is an attempt to pick up only the light with a wavelength corresponding to space between the mirrors using the resonance of light between mirrors (Fizeau interferometer).
This method is effective in that the displayed color is changed using the actuator driven by an electric signal. However, it requires use of actuators in at least two positions to drive the mirror for each pixel. Difficulties are found in high density arrangement of minute pixels and in the production of a high definition display element.
In the technique proposed in the following document, minute actuators arranged flatly on the sheet, which is not a color display element, are adhered to an organic transistor arrangement. When they are driven, the actuators (benders) are displaced independently from each other, and display in braille is given in real time: Kato, Iba, Sekitani, Noguchi, Hizu, “A Flexible, Lightweight Braille Sheet Display with Plastic Actuators Driven by An Organic Field-Effect Transistor Active Matrix”, IEEE International Electron Devices Meeting, Washington, D.C., Dec. 5-7, 2005, #5.1, pp. 105-108.
This method of using actuators may be used for color display and change of the displayed color. However, as can been seen from the fact that a bent type actuator is used to gain the amount of displacement, this method has a limit of its own and production of a high-definition display element is difficult.
As described above, various problems are involved in the method of displaying a desired color of R, G and B by an independent display element. These problems are exemplified by restrictions on the constituent elements, manufacturing difficulties, limited resolution, difficulties in producing a high-definition product and problems with increased area.